As we reached the edge of the loch I saw out upon a small islet in the centre a ruined castle, a long, almost unbroken, grey wall of uniform height, without turrets or battlements, occupying the whole of the islet. Below the walls a few bushes grew from the water's edge, but it was as dreary and isolated a spot as I had ever seen. Beyond stretched the big, dull sheet of water, backed only by the low, uninteresting moorland, the only break in the all-pervading flatness and monotony being afforded by a few wind-stunted trees on the right of the road, and a small dark plantation ahead. When the car had stopped and we had got out and walked a few yards, Ray said: "Yonder is the old castle of Lochindorb, Jack. Behind those walls is the shed which shelters the Kershaw aeroplane. Look!" And gazing in the direction he indicated, I saw a skiff with three occupants coming across from the shadows on the left towards the island. The man steering was a corporal of engineers in khaki. "It appears," Ray went on, "that the machine takes her flight from the open surface of the loch, which, as you see, is about two miles long. She enters and leaves the shed by water." As we were speaking, a bearded gillie of gigantic stature came up from nowhere and promptly ordered us away, an order which we were very reluctantly compelled to obey. At last, however, we had discovered the obscure spot where the secret trials were in progress. "I knew from the first that the tests must be in progress in this district," Ray said, "for a month ago that motor engineer in Grantown of whom you hired your cycle made a small part of a new motor for a man who was a stranger. The part was broken, and the stranger ordered another to be made. I learnt that the first night we were in Grantown." He resolved to spend that night at Grantown, therefore we dined together, and when we rose from table he went to his room in order to obtain his pipe. [Illustration: THE NEW BRITISH ARMY AEROPLANE: ROUGH SKETCH DRAWN BY LIEUT. KARL STRAUS, OF THE GERMAN SECRET SERVICE.] Ten minutes later he returned, saying: "Just come with me for a moment, Jack." I rose and followed. We ascended the stairs, and passing along the corridor he halted before the door of No. 11 and tapped at it quietly. It opened, and Smith stood upon the threshold. "I wish to speak with you a moment," Ray said, facing him determinedly. The man's face fell. We both entered, but so surprised was he that he could utter no protest. We saw that on the table beneath the lamp was spread a number of photographs and papers. He had been writing upon a sheet of foolscap and the writing was in German. "Yes," exclaimed Ray in a tone of satisfaction as he bent over to glance at the first few lines. "I see. You report: 'The upper plane is somewhat curved, with an----'" "What's my business to do with you, pray?" the man asked defiantly in excellent English.